The present invention relates generally to three dimensional (3D) computerized tomography (CT). More particularly, the present invention relates to an arrangement for imaging relatively large objects with relatively small area detectors.
In conventional computerized tomography for both medical and industrial applications, an x-ray fan beam and a linear array detector are used. Two-dimensional (2D) imaging is achieved. While the data set may be complete and image quality is correspondingly high, only a single slice of an object is imaged at a time. When a 3D image is required, a stack of slices approach is employed. Acquiring a 3D data set one 2D slice at a time is inherently slow. Moreover, in medical applications, motion artifacts occur because adjacent slices are not imaged simultaneously. Also, dose utilization is less than optimal because the distance between slices is typically less than the x-ray collimator aperture, resulting in double exposure to many parts of the body. In 2D CT, the scanning path of the source is often a simply circular scan about the object. The linear array detector is fixed relative to the source. (Although it is usual to talk about a scan path of a source relative to the object to be imaged, it is to be appreciated that the object may be rotated or otherwise moved to provide relative motion between the object and the source.)
In a system employing true cone beam geometry for 3D imaging, a cone beam x-ray source and a 2D area detector are used. An object is scanned, preferably over a 360.degree. angular range, either by moving the x-ray source in a scanning circle or other path about the object or by rotating the object while the source remains stationary. In either case, the area detector is fixed relative to the source. The relative movement between the source and object which is to be imaged provides scanning in either case. Compared to the conventional 2D stack of slices approach to achieve 3D imaging, the cone beam geometry has the potential to achieve rapid 3D imaging of both medical and industrial objects with improved dose utilization.
The 2D area detector used for 3D imaging generally has detector elements arranged in rows and columns. Such area detectors, using an array of detector elements, have had either flat or curved geometry. In other words, the rows and columns have been arranged in a plane for flat geometry detectors and have been arranged in curves for curved geometry detectors. Available area detectors have generally been of large size and low quality, such as x-ray image intensifiers, or of small size and higher quality. High costs and other factors have made high quality, high resolution, large area 2D array detectors generally unavailable.
U.S. Pat. No. 5,032,990, issued Jul. 16, 1991, entitled "TRANSLATE ROTATE SCANNING METHOD FOR X-RAY IMAGING," assigned on its face to the assignee of the present application, and hereby incorporated by reference, discloses a technique for two-dimensional imaging of an object which is so wide that a linear array detector is not wide enough to span the object or part which is to be viewed.
U.S. patent application Ser. No. 07/577,163, RD-19,682, filed Sep. 4, 1990, in the name of Eberhard and Tam, entitled "CONE BEAM SCANNING TRAJECTORIES FOR THREE-DIMENSIONAL COMPUTERIZED TOMOGRAPHY DATA ACQUISITION WHERE OBJECT IS LARGER THAN THE FIELD OF VIEW," assigned to the assignee of the present application, and hereby incorporated by reference discloses a technique for avoiding corrupted data when performing 3D CT on an object larger than the field of view. (No representation is made or intended that this referenced application is necessarily prior art to the present application.)